I am trying to test the effects of wall rougness in straight pipes in FLUENT but the results are not compatible with corresponding values in literature. For instance, I have a 50-millimetre-diameter pipe with water flowing through it at about 2 m/s. I want to compare two cases, a smooth pipe and a pipe of roughness k = 0.01 mm. When I run the calculation, though, the results are almost identical (f1 = 0.017459, f2 = 0.017462) whereas the literature values differ significantly (f1 = 0.01738, f2 = 0.019054607). Might this only be due to the mesh being too coarse? At least the result for the smooth pipe resistance coefficient is very near to the literature value. I assume the variable roughness hight is FLUENT corresponds to the standard roughness values given in mm.